Documenting your source code is always a good idea, whether it is an internal project or external software that will be used by other developers. Internal projects suffer because of developer turnover and often poor, or little to no documentation available to help new developers get up to speed. Many third-party APIs fail to get off the ground or uptake is slower than expected, often with adopters abandoning the APIs through frustration because of the poor state of the developer documentation.
It is always a good idea to include copyright notices at the top of each source code file and to comment on your namespaces, interfaces, classes, enums, structs, methods, and properties. Your copyright comments should be first in the source file, above the using statements and take the form of a multiline comment that starts with /* and ends with */:
/*********************************************************************************...